An outboard motor is attached to the stern of a boat through a stern bracket, so that the outboard motor can swing in the lateral direction about a vertical axis and also tilt up and down about a horizontal axis. The outboard motor has an engine for driving a propulsion unit to propel the boat via a screw-propeller of the propulsion unit. The engine, engine accessories, a drive shaft, a gear mechanism and the screw-propeller are supported by a case means or assembly, and the engine is covered by a cover means or structure.
The cover structure defines an engine room in which the engine is installed. The cover structure includes a top cover that covers an upper part of the engine, and an under cover that covers both a lower part of the engine and a mount case on which the engine is mounted. The top cover is also called an engine cover. When the engine needs heavy maintenance, both the engine cover (top cover) and the under cover are removed. However, as for the light maintenance of the engine including inspection of ignition plug units, it is quite cumbersome for the operator to remove both the engine cover and the under cover and reassemble them together. To deal with this problem, several improvements have been proposed as disclosed, for example, in Japanese Patent Laid-open Publications (JP-A) Nos. HEI-10-184376 and HEI-8-99693.
The prior proposal shown in JP-A-HEI-10-184376 includes an under cover having a cutout recess formed at a rear end portion of the under cover. The cutout recess has a horizontally elongated U-shaped configuration for allowing access to an engine. A lid is removably connected to the under cover so as to close the U-shaped cutout recess. For attachment to the under cover, the lid has on its inside surface a plurality of mounting brackets connected by screws to corresponding retainers formed on an inner surface of the under cover along the U-shaped cutout recess. The U-shaped cutout recess allows access to the engine without removing the under cover and hence increases the efficiency of the maintenance work. However, since the screws used for attaching the lid to the under cover are disposed vertically and form joint portions on the interior side of the under cover, this arrangement still requires a top cover to be removed before the lid is detached from the under cover to open the U-shaped cutout recess.
Another prior proposal shown in JP-A-HEI-8-99693 comprises an under cover having circular holes formed in a rear end portion thereof. Through the circular holes, a tool is inserted into an engine room for tightening or loosening screws used for connecting a cylinder head to a cylinder block of an engine. The holes are normally closed by rubber plugs. The under cover has a dish-like structure and may be formed by a mold assembly that can be opened and closed in a vertical direction. The holes in the under cover are formed by slide cores associated with the mold assembly so as to be movable in a direction perpendicular to the opening and closing direction of the mold assembly. Due to the presence of the slide cores, the mold assembly as a whole is relatively complicated in construction and expensive to manufacture. Another problem is that the size of the holes is as small as possible because the holes lower the rigidity of the under cover.